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  <script>
    // 题目1(选做)：const arr=['name','age','hhh','hhh','age','hhh','hhh','hhh']各出现多少次
    // 要求输出一个对象如下：{age: 2,hhh: 5,name: 1}
    const arr = ['name', 'age', 'hhh', 'hhh', 'age', 'hhh', 'hhh', 'hhh']

    const countNum=(arr)=>{
      let o={}
      arr.forEach((value,key) => {
        if(o[value]){
          o[value]++
        }else{
          o[value]=1
        }
      });
      return o
    } 
    console.log(countNum(arr))

    // 题目2(必做)：现在两个数组，判断在a中的元素，不在b中 const a = [1,2,3,5] const b=[1,3,5,6] 将在a不在b中的筛选出来
    // 要求：输出一个数组：[2]
    const a = [1, 2, 3, 5]
    const b = [1, 3, 5, 6]

    const filterValue=(arr1,arr2)=>{
      let newarr=[] 
      arr1.forEach(value => {
        if(arr2.indexOf(value)===-1)newarr.push(value) 
      });
      return newarr
    } 
    console.log(filterValue(a,b))

    // 题目3(必做):数组去重(可以用多种方法,至少写一种)
    // 要求：输出一个数组：[1,2,3,9]
    const arr2 = [1, 2, 3, 2, 9]

    const remDuplicate=(arr)=>{
      let newarr=[] 
      arr.forEach(value => {
        if(newarr.indexOf(value)===-1)newarr.push(value) 
      });
      return newarr
    } 
    console.log(remDuplicate(arr2))
  </script>
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